1. Field of the Invention.
The present invention relates to a nonmagnetic nickel tungsten cemented carbide composition which exhibits nonmagnetic properties independent of the free carbon level of the composition.
The present invention further relates to a nonmagnetic nickel tungsten cemented carbide composition which is useful for making wear resistant parts in electronic instruments.
The present invention further relates to a nonmagnetic nickel tungsten cemented carbide composition which is useful for making punches to deep draw aluminum beverage cans.
2. Description of the Related Art.
Nemeth et al., U.S. Pat. No. 3,918,138 describes compositions for producing nonmagnetic cemented carbides based upon Ni binders. In general, Ni is the least magnetic among the ferromagnetic elements. Ni-binder cemented carbides are thus usually "weakly" magnetic. Nemeth '138 adds Ti to render the Ni-binder cemented carbides completely nonmagnetic. The drawback to Ti addition is a that Ti is a very strong carbide former, and hence Ti addition will invariably de-carburize the WC present in the cemented carbide. This may lead to the formation of highly undesirable brittle eta-phase by forming Ni2W4C. Thus, a carbon lean condition is a prerequisite for obtaining nonmagnetic behavior in cemented carbides containing Ti additions. In other words, free carbon cannot be present in nonmagnetic cemented carbides based on Ti additions.
The present invention uses Cr to form nickel tungsten cemented carbide compositions that are nonmagnetic independent of the free carbon level and without forming a brittle eta phase.
Hong, U.S. Pat. No. 4,963,183 discloses a corrosion resistant cemented carbide wherein chromium is added to cemented carbide to enhance corrosion resistance. Hong did not recognize that the addition of chromium affected the magnetic properties of the composition.
Lindholm, U.S. Pat. No. 4,497,660 discloses the addition of Cr to NiWC cemented carbides as a means for improving the corrosion resistance of such hard metal carbides. Nowhere does Lindholm recognize the ability of chromium to affect the magnetic behavior of Ni WC cemented carbides.
Ekemar et al., "Nickel as a Binder in WC-Based Cemented Carbides" Journal of Refractory and Hard Metals, Mar. 1983, is an article directed to the use of chromium to provide corrosion resistance to Ni WC cemented carbide compositions. There is no showing of the use of Cr in Ni WC cemented carbide compositions to affect the magnetic properties of it.